Time division multiple access (TDMA) techniques provide a large number of communication channels for telephony services and are optimal for peaky environments. The load in each satellite beam can be peaky due to high densities of subscribers in metropolitan areas. TDMA access schemes allow frequency assignments to be reallocated from low utilization beams to hot spots. TDMA systems are therefore optimal for coverage in the western United States where cities tend to be more widely separated than cities on the eastern United States.
Code division multiple access (CDMA) techniques are used to provide services requiring more uniform, non-peaky loaded services to take advantage of the CDMA reuse factor and variable data rate services. CDMA is optimal for uniform density environments and is optimal for coverage in the eastern United States and Europe where metropolitan areas overlap.
There is a significant need for a multi-mode system and subscriber unit that are able to use both TDMA and CDMA techniques based on the current usage or the load on the system.